The ideal geometric configuration of a four wheel vehicle is a rectangle in which: the steerable wheels will run parallel with each other and are equidistant from the center of the connecting axle or its equivalent; in which the non-steerable wheels will run parallel with each other and are equidistant from the center of the connecting axle or its equivalent; in which the non-steerable wheels either track with the steerable wheels or are equally off set from the steerable wheel tracks; and in which the vehicle body has its longitudinal geometric center line coincident with the longitudinal center line for the steerable and non-steerable wheels.
The practical and economic considerations involved in the production of wheeled vehicles taken into account the complications in connection with manufacturing tolerances present in the various parts and the possibility that tolerance mis-matching can build up variations from the ideal geometric configuration. As a consequence of the possible mis-matching of tolerances in the parts making up a finished vehicle provision is made for mechanically adjusting wheel positions relative to the chassis or body of a vehicle. In some vehicles all adjustments are found in the steerable wheel assemblies, while in others the adjustments are provided in both the steerable and non-steerable wheel assemblies. Generally vehicles are permitted to have some deviations from the ideal conditions of wheel alignment and wheel to body alignment. As along as the deviations are not regarded as serious the vehicle is put into use.
Wheel alignment apparatus has been disclosed by Manlove U.S. Pat. No. 3,181,284 of May 4, 1965 in relation to the steerable and non-steerable wheels of a vehicle. The objective of this disclosure is limited to mechanical apparatus in which mounting members are connected to the rim of the vehicle wheels without being compensated for run out or for mechanical variations in the shape of the wheel rims, and in which wheel alignment measurements are made from positions of the measuring apparatus which is displaced from positions representing the true alignment measuring positions. Vehicle wheel alignment apparatus of the electronic type is disclosed by Florer in U.S. Pat. No. 4,095,902 of June 20, 1978, by Lill in U.S. Pat. No. 4,097,157 of June 27, 1978, and by Senften in U.S. Pat. No. 4,126,943 of Nov. 28, 1978.
In connection with the hereinafter to be described wheel compensating means, advantage is taken of the run out compensator method disclosed in Senften U.S. Pat. No. 3,892,042 of July 1, 1975.